1. Field of the Invention
The present invention relates to a radiation detection apparatus and a system, particularly to a radiation detection apparatus and a system used for X-ray detection apparatus in medical and industrial non-destructive inspection use.
In the present specification, description will be made on an understanding that radiation includes also electromagnetic waves such as X-ray, α-ray, β-ray and γ-ray.
2. Related Background Art
FIG. 10 is a schematic plan view of a pixel of a radiation detection apparatus known in the related art, FIG. 11 is a cross-sectional view along a line 11—11 in FIG. 10, and FIG. 12 is an equivalent circuit diagram of the apparatus shown in FIGS. 10 and 11.
In the following, there will be given a brief explanation on the function of the radiation detection apparatus known in the related art. In such radiation detection apparatus, a phosphor (114) formed under a protective layer (115) converts a radiation into a light, and a photoelectric conversion unit (108) provided on a glass substrate (101) converts such light into a charge, which is accumulated in a capacitance C1 constituted by the photoelectric conversion unit (108).
A TFT unit 1 (107) is activated to output the charge, accumulated in the capacitance C1, through a signal line (113) to an external unrepresented signal processing unit.
The TFT unit 1 (107) and the photoelectric conversion unit (108) are formed on the glass substrate (101) at the same time.
In the following, there will be given an explanation on a method for producing the radiation detection apparatus shown in FIGS. 10 to 12.
At first, a gate metal film composed for example of Al or Cr is formed by sputtering or evaporation method, and is then patterned and etched by a photolithographic process to form a gate wiring portion (102), a lower electrode (102′) of the photoelectric conversion unit (108) and a gate electrode (102″) of the TFT unit 1 (107). The etching process is executed by both wet etching and dry etching.
Then a gate insulation film (103) constituted by SiN, SiO2 etc. is deposited by plasma CVD method (chemical vapor deposition) utilizing silane, ammonia, hydrogen, TEOS etc. as the source materials.
Then a semiconductor layer (104) with amorphous silicon (a-Si:H), polysilicon etc. is deposited in succession by plasma CVD method with silane and hydrogen as the source materials. In this process, the semiconductor layer (104) has to be formed thick (for example 400 to 1000 nm) in order to convert therein the light into a sufficient electrical signal.
Then an ohmic contact layer (105) is deposited in succession by plasma CVD method. As the ohmic contact layer (105), there is employed amorphous silicon or microcrystalline silicon (μc-Si) formed with silane and hydrogen as the source material gases, and phosphine gas(PH3) etc. is used as a doping gas during the film deposition.
Then an isolation process is executed by patterning and etching in a photolithographic process thereby forming the photoelectric conversion unit (108) and a thin film transistor unit (107).
Then a film of a wiring metal of Al, Cr etc. is formed by sputtering method, and an etching is executed to form a source electrode (109), a drain electrode (106), a signal line (113), and a driving wiring (bias wiring) (110). The signal line (113) is connected to the drain electrode (106).
There are further formed thereon a protective layer (112) of SiN, PI etc. for stabilizing the device characteristics, and a phosphor of a material (114) such as GOS, CsI etc. for converting X-ray into light. The X-ray enters from a direction indicated by an arrow (111), and is converted by the phosphor (114) into a visible light, which is subjected to a photoelectric conversion in the semiconductor layer (104) of the photoelectric conversion unit (108). On the phosphor (114), there is formed a protective layer (115) such as of PET.
Also a radiation detection apparatus for directly converting X-ray into a charge is disclosed for example in Japanese Patent Application Laid-Open No. 11-44764.
However, such known art still has a room for improvement for taking a moving image, and is associated with a drawback of taking much time to transfer and reset signals. Especially at higher frame rate, charge readout cannot be executed due to the short detection time.
Therefore, an object of the present invention is to provide a radiation detection apparatus suitable for capturing a moving image.